Stripping

Stripping

Paint & Body Basics

Stripping

Unless the car you're working on has only one prior paint job, and it's still in good shape, you should figure on stripping the surface to metal. This may sound excessive, but again, the cars we usually deal with have been around a long time, and very few of them have original paint. Several re-sprays later, there's no telling what sins have been concealed. Even if the body itself is free of damage and filler but has the remnants of a few paint jobs, it's best to get them all off. Most of the old OEM paints are not very stable to put a new urethane paint job over the top of. Removing that paint can be accomplished in several ways, from basic sanding to high-tech chemical stripping. These are your options:

Sanding

This is the most basic means of removing old paint from your car, but it's also the most tedious and time consuming. However, it is the least damaging to the car and if the current finish on your car is thin or peeling, it may not take much effort with a sander to get it down to bare steel. If you go this route, you'll probably be using a dual-action or "DA" sander. They have an orbital action and a stripping action. Lock your DA sander into stripping action and start with 6 inch-80 grit DA paper. 6 inch is by far the most universal and most commonly used. Some DA’s can’t handle an 8 inch. Remember, using any heavier paper will put in scratches that you will have to remove or cover up later. Plus, heavier grits can cause excessive heat causing your panels to warp. This is why we use a DA and not a grinder. Get yourself a box or roll of self adhesive paper to strip the car. 3M makes a real nice air operated DA with a vaccum bag that will capture almost all of the sanding dust.

MECHANICAL STRIP

Clean with the appropriate cleaner.

Remove paint with 80 grit. Avoid 36-40 grit disc because it leaves too deep of a scratch in the metal.

PROS • Removes old body work • Safest way for do-it-yourself

CONS  • Time consuming and surface rust • Labor

Chemical Stripping

This approach entails applying a chemical to the surface, which then softens and lifts the paint. After the product has done its thing, the bubbled paint must be scraped off of the surface and discarded. Hint :If you take a garbage bag, rip it open, laying it across the fresh stripper. This will hold the solvent in and allow for better solvent penetration into the paint. When done you can then flip the bag over laying it on the ground and scrap the stipper and old paint into it, then tie it up and throw the bag away. Some of the strippers are thick and must be brushed on while others can be sprayed, either from aerosol cans or pump bottles. The best approach is to strip in small sections, as there is usually a time window when the paint is fully softened. If you wait too long, the bubbled paint will begin to harden again, making it more difficult to scrape off. Like sanding, chemical stripping will take time, and cars with multiple paint jobs will require multiple applications before bare metal is reached. You should keep any strippers away from any edges, seams and trim. If stripper gets behind any of these areas, it can come back out on you later on and stain or strip your new paint job. Some strippers are safe to use around rubber and chrome trim while others can damage these items, so be sure you know what you're dealing with before you begin. Also, some stripping products are intended for specific types of paint, like enamel, lacquer, and so on, so shop wisely. Do not use standard strippers on any fiberglass products (like boats or Corvettes), they can eat into the gel coat. Use only a fiberglass stripper. When done with stripping, wash very well with soap and water. Then you can take your DA and sand around all the edges. Strippers have a very strong chemical oder, use them only in well ventilated areas and wear strong chemical resistant gloves. Aircraft stripper is the strongest and most commly used. They also make some low oder stripper, but they don't seem to be quite as effective. They also build specialty strippers like lacquar strippers that will only take it down to the primer, fiberglass strippers that don't damage gelcoat and urethane strippers that won't damage urethane bumpers.

Chemical Dipping

If chemical paint-stripping sounds like a good idea for your car but you'd rather remove yourself from the process, consider chemical dipping. As the term implies, the entire body of the car will be dipped in a vat of chemicals to remove all of the finishes, leaving it in bare steel. This service is provided by businesses that specialize in this type of work, and these places usually don't do any of the work to prepare the car for dipping, like removing everything that isn't the body itself. You'll have to handle that yourself, and you'll need to remove everything from the body prior to dipping, including the glass, brightwork, and all interior trim. In fact, even the remaining weatherstripping, seam-sealer, and undercoating will be dissolved. Some car-builders have concerns about chemical dipping, feeling that it can leave inaccessible areas--like the insides of the rocker panels--untreated and vulnerable to future rusting. However, dipping facilities that are equipped for treating car bodies usually pass the shell through multiple vats, including one that should leave an etched coating on the steel, protecting it from moisture. Despite this, you should be prepared to work on the body immediately after it is returned. Leaving the bare body anywhere after stripping will start the rusting process. Dipping is an excellent means of stripping, but it isn't right for every job. Obviously, if you didn't intend to completely dismantle your car and replace all of the weatherstripping, window seals, body seam sealer, and so on, this isn't the option for you. However, if you do select this method, consult with the stripping facility first to find out what they plan to do, and what they expect you to do before dropping the body off. Some dippers will reject a body that's too greasy or has excessive loose rust, as this can contaminate the dip.

CHEMICAL PAINT REMOVERS

Aircraft strippers (Must be neutralized with water) Environmentally Compliant 

PROS • Best for original paint

CONS • Messy job, leaves metal smooth • Does not remove rust • Slow for cars with multiple paint jobs • Does not remove body filler

Blasting

One of the more popular means of having a car stripped is blasting--the process of using compressed air to shoot media particles at the body to abrade the finish. The most common form of pressure-blasting uses sand. However, sandblasting is not recommended for sheet metal auto bodies, as the sand can be too aggressive. Even when fine sand is used, it can still warp the sheet metal, since the abrasion quickly builds heat that can distort the steel. A better method of blasting sheet metal involves using plastic media. The small plastic particles usually have sharp edges that are very effective at stripping paint, yet the plastic won't create heat when it contacts the steel surface, so warpage isn't an issue. Although, this will take off paint, it will not remove any rust. This will need to be done a different way. Usually, a car body will be completely dismantled prior to blasting, though it isn't absolutely necessary, as it is with dipping. Glass and other trim can be covered for media-blasting. Unfortunately, this media does end up in virtually inaccessible places, so this is certainly a concern.

MEDIA BLAST

The dry method is preferred and is becoming more popular. Should be sanded with machine 120-180 grit to remove paint (slight nibs) that can be left behind. To remove remaining rust, those areas will need to be spot sandblasted or wire-brushed.

PROS • Safe way to remove paint • Will not pit or abrade metal

CONS  • Does not remove rust 

Another emerging trend in body blasting is the use of baking soda as the media. The baking soda is also effective at stripping when applied under pressure, though it is pressurized with water rather than air. This process, considered wet pressure blasting, does not create dust and is not harmful to glass and trim. As a bonus, disposing of the baking soda can be as simple as washing it down the sewer, as some cities actually appreciate the addition of the baking soda to sewage since it will neutralize acids. Like media-blasting, baking soda blasting is a professional service, not a DIY deal.

With any of the blasting processes you will have a layer of fine dust everywhere. You will need to make sure that you blow the dust out of all of the seams and cracks so that it does not fly out into your paint job when you come by with your spray gun. After stripping, get a layer of epoxy or etching primers on the bare steel to protect it. Then you can work on the project a little at a time.